Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$45.82	6.472%	$48.7855	$48.79	$48.80	$48.80
Purchase #2	$98.94	5.802%	$104.6805	$104.68	$104.70	$104.70
Purchase #3	$215.26	6.340%	$228.9075	$228.91	$228.90	$228.90
Purchase #4	$242.69	13.340%	$275.0648	$275.06	$275.05	$275.10
Purchase #5	$136.64	3.473%	$141.3855	$141.39	$141.40	$141.40
Purchase #6	$176.54	7.830%	$190.3631	$190.36	$190.35	$190.40
Purchase #7	$168.71	12.199%	$189.2909	$189.29	$189.30	$189.30
7 purchase totals =	$1,084.60		$1,178.4778	$1,178.48	$1,178.50	$1,178.60